Now, though, it's expected to sit still more than ever. Fewer activities that allow kids to blow off steam.
Different acculturation.
We can even make the case that once a set of behaviors has been classed as a "disease" it's easier to spot, easier to record, and, well, who doesn't want to blame something external to their kid for their kid's problem?
Oddly, though, the entire ADHD diagnosis pattern has long been noticed to not only be increasing over time, but to have a geographical skew. http://www.cdc.gov/ncbddd/adhd/prevalence.html
Lately it's probably also true that a shorter attention span has been producing more problems--you have to *build* attention capacity, and for the last 40 years everything we've been making our kids do and watch has been aimed to satisfying that need of the mammalian brain for short, fast, bright colored things. Movies, games, modes of interaction. It sells movies, music, and services--but in the long term it's a crappy idea. It used to be that you could count on average attention span being age + 5 minutes, I think it was. Good luck getting the average 15-year-old to have a 20-minute attention span.
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